In the perpendicular magnetic recording method, the easy axis of magnetization of the magnetic recording layer, which in conventional media is directed within the plane of the media, is directed in the direction perpendicular to the media; as a result, the demagnetizing field in the vicinity of the magnetization transition region, which is the boundary between recorded bits, is decreased, so that the higher the recording density, the more magnetostatically stable the recorded state, with improved resistance to thermal fluctuations; hence the method is appropriate for increasing areal densities.
When a soft magnetic underlayer, consisting of soft magnetic material, is provided between the substrate and the perpendicular magnetic recording layer, the functions of so-called perpendicular double-layer media are obtained, and excellent recording performance can be obtained. At this time, the soft magnetic underlayer serves to provide a return path for the recording magnetic field from the magnetic head, and can improve the recording and reproduction efficiency.
In general, perpendicular magnetic recording media is configured with a soft magnetic underlayer provided on a substrate, on which are formed, in order, an soft magnetic underlayer which directs the magnetization easy axis of the magnetic layer to be perpendicular to the plane of the substrate, a perpendicular magnetic recording layer consisting of a Co alloy, and a protective layer. However, in recent years, the WATE (for Wide Area Track Erasure, or Wide Adjacent Track Erasure) phenomenon has come to be recognized as a problem in perpendicular magnetic recording media. The WATE phenomenon is a problem specific to perpendicular magnetic recording media, and is a phenomenon in which, when a signal is recorded in a particular track, signals are demagnetized over a broad area extending for several μm from the recorded track. Methods for alleviating the problem, mainly through the structure or magnetic anisotropy of the soft magnetic underlayer, have been proposed (see for example Patent Reference 1).
It is also proposed that aligning the direction of the magnetization easy axis of the soft magnetic underlayer in particular in the substrate radial direction is effective for the above problem. Following methods are proposed for realizing this magnetic structure;                1) depositing the soft magnetic underlayer under a magnetic field in the radial direction        2) stacking a soft magnetic layer and an antiferromagnetic film as a soft magnetic underlayer (see for example Patent Reference 2 and Patent Reference 3).        
Common method to align the magnetization easy axis direction of the soft magnetic underlayer in the radial direction is to deposit the soft magnetic underlayer in a magnetic field from a magnetron, which generates radial magnetic flux and is placed concentric to the substrate. This method is not effective for a small substrate, particularly for commercialized one with a diameter of 26 mm or 22 mm. When films are deposited simultaneously on the plurality of small substrates, deposition under an uniform magnetic field is difficult and consequently the direction of the magnetization easy axis of the soft magnetic underlayer is directed in various directions.
Patent Reference 1: Japanese Unexamined Patent Application, First Publication No. S58-166531
Patent Reference 2: Japanese Unexamined Patent Application, First Publication No. H06-103553
Patent Reference 3: US 2002/0028357
In addition, film deposition in a magnetic field entails the following problems.
(1) It is difficult to control the magnetic field uniform in the entire radial direction.
(2) The magnetic field is smaller in the inner-periphery portion of the substrate.
As media sizes continue to grow smaller in future, (2) is anticipated to become a serious problem.
Annealing process under a magnetic filed is also proposed for this problem, including the stacking of MnIr antiferromagnetic layer in the soft magnetic underlayer. However, this process needs relatively high temperature and results in the degradation in the magnetic properties of the soft magnetic underlayer and the perpendicular magnetic recording layer. When the soft magnetic underlayer, which is magnetized uniformly in the radial direction, is used, read-write characteristics, especially for the SNR (signal-to-noise ratio) are degraded.
This invention was devised in light of the above circumstances, and has as an object the provision of perpendicular magnetic recording media enabling recording and reproduction of information at high densities, and a method of manufacture and magnetic recording and reproducing apparatus for such media, drawing on a reanalysis of the action of magnetic anisotropy in the soft magnetic underlayer.